Conventionally, a sintered body of cubic boron nitride has large hardness, and accordingly, it has been widely used as a material for tools, such as cutting tools. Furthermore, it is also known to form a surface coating layer on a surface of a sintered body of cubic boron nitride for improved wear-resistance and the like.
For example, Japanese Patent Laying-Open No. 2005-047004 (Patent Literature 1) discloses a composite large hardness material for a tool that is a sintered body of cubic boron nitride having a surface provided with an intermediate layer formed of a compound of a nitride, carbide or the like of group 4a, 5a, and 6a elements, and a coating of TiAlN or the like on the intermediate layer. Furthermore, Japanese Patent Laying-Open No. 2002-144110 (Patent Literature 2) discloses a tool of a surface-coated sintered body of boron nitride that is formed of a sintered body of boron nitride having a surface provided with an intermediate layer formed of at least one element selected from group 4a, 5a, and 6a elements, and a hard coating layer on the intermediate layer. Furthermore, Japanese Patent Laying-Open No. 2000-129423 (Patent Literature 3) discloses a hard coating formed of a first layer formed on a substrate and formed of metal of groups 4a, 5a, 6a, and a second layer formed on the first layer and formed of TiAlVN or the like.